Electrodynamic transducer and connector therefor



Jan. 16, 1951 H. F. HOPKINS ETAL ELECTRODYNAMIC TRANSDUCER AND CONNECTOR THEREFOR Filed April 23, 1945 H. F HOPKINS 7095' R. E. PRESCOTT WM 6. Midi ATTORNEY Patented Jan. 16, 1951 EIJEC'IR'ODYN'KMIC TRANSDUCERQAND- CONNECTOR THEREFOR.

Harris Hopkins, Chatham andltobert'EiPrescott, Murray Hill, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York; N. Y., a corporation of New York Application April 23, 1945, Serial No. 589,884

6 Claims. (01. 179-1155) This invention relates to vibrator systems and more particularly to diaphragm assemblies for electromechanical transducers such as, .for example, transmitters and receivers of the moving coil type.

Electromechanical transducers such as acoustic devices of the moving coil type comprise, in general, a vibratory member, such as a diaphragm and an electrical element, such as a signal coil, coupled thereto for converting vibrations :of the member into electrical signals or conversely, converting electrical signals into vibrations. A major problem involved in the construction of such devicesis that of establishing electrical connection between the electrical element and a circuitto be associated therewith. It is highly desirable that such connection be of low resistance, capableof Wihstanding repeated fiexure or vibration without impairment and of such character as not to affect deleteriously the vibrating characteristics of the assembly.

and substantially no effect upon. the vibrational characteristics of the vibratory member. 7

A further object of this invention is to simplify and facilitate the construction of diaphragm and signal coil assemblies for electroacoustic transducers of the moving coil type.

Still another object of this invention is to increase the ruggedness of such assemblies thereby to minimize damage thereof during manufacture, assembly and transportation.

In one illustrative embodiment of this invention, in a diaphragm and signal coil assembly for moving coil transducers, the diaphragm being of a normally non-conducting material, leading-in connection to the coil is establishedthrough restricted areas of the diaphragm treated to render them electricall conductive. Specifically, in one illustrative construction, the diaphragm is of a fibrous material, such as a fabric, and restricted portions thereof, for example portions extending radially from adjacent the region at which the signal coilis coupled'to'the diaphragm toiadjaecent the periphery of the diaphragm, are im:-' pregnated with. a finely divided conductive material in. a suitable vehicle, for example with inetazl powder loaded resin, and the coil endsare connected tozthese portions; 7 4 The invention and the-seweral features thereof'will Ebe understood mcre-iclearly-and fulIy'T-rom the following detailed description. with reference to the accompanying-drawing Fig. 1 a side viewpartly 11125611171011 'of'a Iliaphragm assembly illustrative of oneeembcdiment of thisinventiongand Fig. 2 is a plan view 'ofthe assembly-zshownin Fig.1. 1

Referring now to *the'drawing; the diaphra m assembly ccmprisesa diaphragmhaving a-central. dished relatively rigid portion l0, iaxperipheral mounting portion .H and an intermediate flexible portion l2 which maybe-corrugatedas-ilius trated. Afilxed to the diaphragm adjacent the junction of thecentral and. intermediate portions [.0 and t2" respectively, is 'a cylindrical form or support It upon which a signal coil :14 is mounted. The diaphragm may beformed in one pice of asuitable fabric, such as muslin. 'Restrictecl pop-.-

tions thereof, .shownclearlyat i5 in. Fig. 2, are impregnated with a material, such as anital powder loaded in a. suitable, vehicle, to. render these portions electrically conductive. An illus trative impregnating, material which hasqbeen fclundsatisiactory is composed of. finely divided silver 'intheform of polished flakes, in a vehicle ofphenolic resin, such as phenol polyvinyl jbutyrol, the powder constituting, of theondlr of 135,116! cent by weight of'the mixture. The diaphragm ay be impregnatedsubsequentl with a suitable material suchas a phenolic condensation product.

Carried by the diaphragm and in intimate contact with the portions I5 thereof are two pairs of terminals or connectors l6 and H, such as eyelets. 'I'he ends I8 of the signal coil M are suitably affixed, as by soldering, to the eyelets l6; suitable conductors IQ for connection. to an external circuit are affixed to the eyelets l'l.

In use, the diaphragm is mounted uponasuitable support; for example, the peripheral portion ll may be clamped between a pair oflncn conductive rings 20 provided with apertures in which the eyelets I! are positioned. v

The diaphragm assembly may be fabricated in the following manner: The portions l5 of a circular blank of fibrous material, such as muslin, are impregnated with the metal powder loaded solvent or vehicle and dried to remove the vehicle. The blank then is impregnated with the desired material, such as a phenolic condensation product, and dried. Thereafter, the blank is formed and moulded into the desired shape, e. g. into the form illustrated in Fig. 1. The eyelets l6 and I! are installed and the Support I3 with the signal coilv l4 thereon is afiixed in place, as by cementing it to the formed diaphragm. Finally, the coilends 18 are secured, as by soldering, to the eyelets I6. I

It will be noted that the completed diaphragm is of homogeneous construction, being impregnated throughout. From a mechanical impedance standpoint, there is no substantial difference between the portions of the diaphragm impregnated with the metal loaded resin and those impregnated with the phenolic condensation product, so that the portions l5 do not deleaphragm of fibrous material having two spaced portions impregnated with a metal powder loaded vehicle, a pair of terminal members electrically integral with each of said portions, one terminal member of each pair being adjacent the periphery of said diaphragm, and the other terminal member of each pair being adjacent the central portion of said diaphragm, and a signal coil coupled to said diaphragm adjacent said teriously afiect the vibrational characteristics of the diaphragm. These portions, of course, vibrate with the diaphragm so that relative motion between the lead-in connections to the coil and the diaphragm is not present. The portions 15 may be made of .substantial area so that a very low resistance lead-in connection is provided thereby. In a typical case, for example, a resistance of 0.08 ohm was obtained. Hence, power losses in the lead-in system are minimized. Finally, lead-in connections provided in accordance with the invention have been found to have a very long operating life, being capable of continuous vibration at the maximum diaphragm amplitude for long periods, without failure. Although a specific embodiment of this invention has been shown and described, it will be understood, of course, that it is but illustrative and that various modifications may be made in the construction shown without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is: 4

1. A vibratory system comprising a vibratory member having a portion of non-conductive foraminous material impregnated with a vehicle loaded with finely divided metal, an electrical element coupled to said member, and an electrical connection between said element and said portion. v

2. A vibratory system comprising a vibratory member having spaced portions thereof of fibrous material impregnated with a metal powder loaded vehicle, an electrical element coupled to said member, terminals carried by said member and electrically integral with said portions, and electrical connections between said element and said terminals.

3. Adiaphragm assembly comprising a' di central portion, each end of said coil being connected to a respective one of said other terminal members.

4. A diaphragm assembly comprising a fibrous diaphragm having two spaced portions impregnated with a phenolic resin loaded with finely divided metal and the remainder impregnated with a phenolic condensation product, a coil coupled to said diaphragm, and electrical connections between said coil and said portions.

5. A diaphragm assembly comprising a fabric diaphragm having a central portion and a peripheral portion, a first pair of eyelets mounted by said diaphragm and in said peripheral portion, a second pair o1". eyelets mounted by said diaphragm and in said central portion, a signal coil coupled to said diaphragm adjacent said central portion and having its ends connected electrically to said second pair of eyelets, and an electrical connection between each of said second pair of eyelets and a respective one of said first pair of eyelets defined by portions of said diaphragm impregnated with a metal loaded resin.

6. A diaphragm assembly in accordance with claim 5 wherein said met'al loaded resin is phenol polyvinyl butyrol having of the order of. 35 per cent by weight of finely divided silver therein.

HARRIS F. HOPKINS.

ROBERT E. PRESCOTT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain May 13, 1930 

